Reclaimers are machines used to handle materials in bulk, especially ore. Such equipment is used in material storage yards, sea and river ports, and other places where it is necessary to transport large quantities of bulk material.
Reclaimers basically comprise a boom, a bucket wheel, and a translation system. The translation system comprises several trucks and wheels and is responsible for the linear movement of the machine under the rails where it is installed, allowing it to move back and forth.
The boom and the bucket wheel consist of elements responsible for reclaiming bulk material. The bucket wheel is a wheel having several buckets distributed along its radial portion.
The bucket wheel rotates so that, when it is in contact with the stack of material to be reclaimed, it is able to collect the material in its buckets and discharge it into the machine boom, thereby reclaiming it.
The boom consists of a lattice beam, configured to support the bucket wheel at its end. The other end of the boom is fixed to the machine translation system, having two rotating degrees in relation to the system, one parallel to the ground and another perpendicular to the ground.
Such degrees of freedom allow an angular movement of the bucket wheel as well as change its height to the ground. The boom is also provided with a conveyor belt along its structure, which is responsible for transporting the material that was collected by the bucket wheel.
In this way, the amount of material being reclaimed is directly proportional to the speed of rotation of the boom and the speed of rotation of the bucket wheel. In order to measure flow rate, that is, the amount of material being collected, a scale is used.
The scale is always mounted at a reasonable distance from the bucket wheel, generally at the midpoint of the boom conveyor, to avoid interference caused by impact of the material during the transition from the bucket wheel to the boom. This distance between the scale and the bucket wheel causes an average delay time of 10 to 15 seconds to the measurement made by it.
In addition to the delay time of the scale, there are also delay times associated with the acceleration and deceleration ramp of the turning mechanism inverters of the reclaimer, which normally range from 6 to 10 seconds.
Control of these speeds is made by a PID controller that takes these delay times into account and measures the flow of reclaimed material to verify the need for changes in these speeds.
In addition to the boom and bucket wheel turning speeds, there are also other factors that interfere with the material reclaiming flow and are related to the stack or bench of material being reclaimed.
The more stable the reclaiming bench, the better the PID controller response to control the boom turning mechanism speed in order to keep the reclaiming flow equal to a desired value.
However, it is not always possible to obtain this stability because several reasons may cause a sudden change in the behavior of the reclaiming bench. These changes in the bench result in changes in the volume to be reclaimed, requiring a very rapid response from the PID controller.
This rapid response of the flow controller to change the turning speeds is to avoid overflows (machine overloads, that is, a reclaiming flow greater than the recommended one) and avoid loss of productivity during the reclaiming process.
In manual operation of the reclaimer, the operator is able to preview a sudden change in the reclaiming bench and act in advance to control the boom turning speed in order to avoid the occurrence of an overflow. However, semiautomatic operation requires methods to allow the flow controller to anticipate some actions, trying to predict what may happen in the future.
This is a problem in semi-automatic operation, since bench instability may cause a certain tuning speed of the boom, which maintained a reclaiming rate equal to the desired value, to generate overflow at the moment it faces a large increase in reclaiming volume caused by bench instability.
Due to the high delay time between the bucket wheel and the scale, the state of the art reveals controls that use more immediate information so that corrections in the boom turning mechanism speed are made quickly without loss of reclaiming rate.
These corrections in the state of the art use estimated flow-based technologies that use data from hydraulic pressure or electric current of the bucket wheel motor to control the reclaiming rate. This control responds to variation of pressure or current in the bucket wheel, automatically adjusting the turning speed as needed.
However, the problem with this technique is that when this type of control faces problems arising from unstable reclaiming benches, which are mentioned above, the controller cannot deal with response time, which is delayed due to delays caused by the acceleration and deceleration ramps of the turning inverter.
Another solution found in the state of the art for the problem of delay time caused by the acceleration and deceleration ramp of the turning inverters is described in the patent document U.S. Pat. No. 9,073,701 discussed below.
The technique disclosed by the American document uses 2D sensors installed near the bucket wheel, configured to calculate the volume of material to be reclaimed by the bucket wheel. From the calculated material volume, it is possible to predict the reclaiming rate and the ideal boom turning speed for the entire bench to be reclaimed.
In this technique, the 2D sensor reading occurs in advance, that is, before detection by the pressure or current of the bucket wheel, making control of the boom turning speed faster and more efficient. When reading overflow or decrease in reclaiming rate, the PID controller receives information on the turning speed ideal for the given reading, thereby improving its response time.
However, using this technique of document U.S. Pat. No. 9,073,701 requires the acquisition of robust 2D sensors, making its cost very high. Another problem with this technique is that it cannot respond to pile collapses on the bucket wheel because the sensor reading is made only a few degrees in front of the bucket wheel.
The state of the art also includes other patent documents claiming automatic control systems for reclaimers. One such document is CN101776867B, which discloses a method of control for bucket wheel reclaimers.
This method allows to insert data experimentally or analytically obtained in a database in the machine PLC. The control measures the frequencies of the turning motors of both the bucket wheel and the reclaimer boom. With these frequencies the control can verify the stresses on these elements, the speed of their rotation, and the amount of material being reclaimed.
In addition, the control measures the location of all elements that comprise the reclaimer by means of an encoder. With this data, the control is able to measure the translation and rotation movement of its elements.
Data entered include: the geometry of the stack of material being collected; the speed appropriate for the operation in relation to the material being collected; and other information.
Thus, the reclaimer is able to calculate its position relative to the material stack and the modifications made to the material stack during reclaiming.
However, document CN101776867B only demonstrates a technique for automating a bucket wheel reclaimer by means of a solution for detecting the edges of the material stack, using data of stack generated during stacking and data of bucket wheel motor current.
In addition, the material flow is controlled by a control mesh that uses information of bucket wheel current, not being able to improve and control the flow of material based on reclaiming already made.
Thus, it is concluded that both the solution proposed above and the solutions pointed out in patent documents U.S. Pat. No. 9,073,701 and CN101776867B are unable to anticipate control actions to avoid overflows or loss of reclaiming rates.
In addition, none of the devices, systems, and methods in the state of the art are capable of improving the PID response time without using robust 2D sensors.